Effects Of Urban Park On Atmospheric Particulate Matters Dispersion Coupling Field Experiment And Numerical Simulation

Urban park plays a significant role in air particulate reduction in urban environment.In order to explore the distribution of particulate pollution in different landscape spaces of urban park,revel the mechanism of landscape elements and meteorological factors on the change of particulate matters and explore the indicators for urban park vegetation optimum design to improve local air quality.This study conducted on-site measurements and computational fluid dynamic simulations to monitor the particulate concentration and meteorological factors and evaluated the aerodynamic and deposition effects of vegetation enhancement in a public park respectively.On-site measurement:Six different landscape spaces were selected to conduct on-site measurement in an urban park.The air temperature,relative humidity and PM_2.5concentration were monitored during measurement.The relationships between the composition of landscape elements and PM_2.5 concentration in different spaces were analyzed,and the correlations between spatial meteorological factors and PM_2.5concentration were also discussed.The results were as follows:1)There were significant differences?P<0.05?in PM_2.5 concentration distribution among landscape spaces;2)There was a significant negative correlation?R=-0.903?between PM_2.5 concentration and green volume?D?.When 113.57<D<204.81,the PM_2.5.5 concentration decreased slowly with the increase of green volume,while the PM_2.5 concentration decreased significantly when216.78<D<370.38;3)The PM_2.5.5 concentrations of different landscape spaces were related to the range of relative humidity:the greater range of humidity,the higher PM_2.5;4)The lowest concentration spaces with the characteristics of minimum temperature,relative humidity and wind speed range.The results of this research provide theoretical basis and methods for the suitability design of microclimate in different landscape spaces of urban park.Numerical simulation:Firstly,the airflow characteristics and deposition effects of vegetation were predicted and compared with the measured air velocity and particulate matters data to validate the numerical modeling.Secondly,supplementary green areas and associated coverage ratios?tree coverage ratio,crown volume coverage and roof greenings?were added to the computer simulations.After a series of numerical simulations and comparisons,results revealed that:1)Tree coverage and crown volume coverage were closely related to particulate concentration?R²>0.92?.In order to ensure that the concentrations of PM₁₀ and PM_2.5 in the pedestrian space of the park meet the WHO AQGs?IT-1?standard,the tree coverage ranges from 39.8%to 55.1%,and the CVC was 1.8 to 3.4m³/m².2)Compared with roof-free greening,the maximum reduction rate of average particulate matter concentration in roof greening was found in leeward buildings,the maximum reduction rate of PM₁₀ was 7%,and the maximum reduction rate of PM_2.5 was 5%.3)The removal rate of particulate matter is strongly correlated with tree coverage and CVC?R²>0.90?.When tree coverage was 48.3%and 55.5%respectively,PM₁₀ and PM_2.5showed the greatest reduction rate,and when the crown volume coverage?CVC?was 2.6m³/m² and 2.9 m³/m²,the maximum reduction rates of PM₁₀0 and PM_2.5 were 61.7%and 53.9%respectively.As a beneficial supplement for urban green space about particulate reduction research,the results could provide theoretical basis of microclimate suitability design,and also provide scientific guidances for landscape designers in vegetation optimum design with both ecological benefits and aesthetic values achieved in urban parks.